What is the name of the popular Italian street food consisting of a fried pastry filled with various ingredients, often including rice or pasta?

The popular Italian street food you’re thinking of is called arancini. These are typically rice balls that are stuffed with various fillings, coated in breadcrumbs, and then fried. Another similar item is supplì, which is also a rice-based snack but often includes a filling of mozzarella. Both are delicious and widely enjoyed in Italy!